Derivative Instruments and Hedging Activities - Realized and Unrealized Gains or Losses on Commodity Derivatives (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	$ (3)	$ (4)
Total deferred gains/(losses)	(65)	(159)
Net deferred gains/(losses)	(68)	(163)
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income	(49)	(113)
Purchased power expense
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income	0	(114)
Unrealized gain/(loss) on derivatives		(62)
Gas purchased for resale
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income	(63)	(10)
Non-utility revenue
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income	14	11
Non-utility operating revenue
Pre-tax gain/(loss) recognized in income
Unrealized gain/(loss) on derivatives	3	1
Deferred Derivative Gains,Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	0	(4)
Deferred Derivative Gains, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(3)	0
Deferred Derivative Losses, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	0	(30)
Recoverable Energy Costs, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(45)	(73)
Deferred Derivative Losses, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(20)	(56)
CECONY
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(5)	(5)
Total deferred gains/(losses)	(59)	(145)
Net deferred gains/(losses)	(64)	(150)
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income	0	0
CECONY | Purchased power expense
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income	0	0
CECONY | Gas purchased for resale
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income	0	0
CECONY | Non-utility revenue
Pre-tax gain/(loss) recognized in income
Total pre-tax gain/(loss) recognized in income	0	0
CECONY | Deferred Derivative Gains,Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(2)	(4)
CECONY | Deferred Derivative Gains, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(3)	(1)
CECONY | Deferred Derivative Losses, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	1	(28)
CECONY | Recoverable Energy Costs, Current
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	(40)	(66)
CECONY | Deferred Derivative Losses, Noncurrent
Pre-tax gains/(losses) deferred in accordance with accounting rules for regulated operations:
Total deferred gains/(losses)	$ (20)	$ (51)